Communication devices such as wireless communication devices, that simply may be named wireless devices, may also be known as e.g. user equipments (UEs), mobile terminals, wireless terminals and/or mobile stations. A wireless device is enabled to communicate wirelessly in a cellular communication network, wireless communication system, or radio communication system, sometimes also referred to as a cellular radio system, cellular network or cellular communication system. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communication network. The wireless device may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, just to mention some further examples. Wireless devices may be so called Machine to Machine (M2M) devices or Machine Type of Communication (MTC) devices, i.e. devices that are not associated with a conventional user.
The wireless device may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The cellular communication network covers a geographical area which is divided into cell areas, wherein each cell area is served by at least one base station, or Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is typically identified by one or more cell identities. The base station at a base station site provides radio coverage for one or more cells. A cell is thus associated with a geographical area where radio coverage for that cell is provided by the base station at the base station site. Cells may overlap so that several cells cover the same geographical area. By the base station providing or serving a cell is meant that the base station provides radio coverage such that one or more wireless devices located in the geographical area where the radio coverage is provided may be served by the base station in said cell. When a wireless device is said to be served in or by a cell this implies that the wireless device is served by the base station providing radio coverage for the cell. One base station may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless device within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunication System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communication (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to other base stations and may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which may be referred to as 3rd generation or 3G, and which evolved from the GSM, and provides improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices. High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), defined by 3GPP, that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA. Such networks may be named WCDMA/HSPA.
The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into evolved UTRAN (E-UTRAN) used in LTE.
The expression downlink (DL) is used for the transmission path from the base station to the wireless device. The expression uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
Work is ongoing with designing a baseline for the next generation wide area networks, which may be referred to as fifth generation (5G). To reduce energy consumption in the network and to fully enable utilizing high gain beam forming or other multi-antenna techniques a concept has been defined separating the control/broadcast layer from the data plane. The broadcast layer comprises a broadcasted Access Information Table (AIT) and a broadcasted System Signature Sequence (SSS). See e.g. P. Frenger, M., Olsson, and E. Eriksson, “A clean slate radio network designed for maximum energy performance,” in Proc. IEEE PIMRC 2014. FIG. 1a is a time-frequency diagram schematically illustrating how AIT and SSS can relate to each other. The SSS may be used to map information from a broadcasted AIT. The broadcasted signals should be able to send in a Single Frequency Network (SFN) structure. Broadcasted information may contain parameter settings related to how to access the system, through random access, and be reached by the system, by means of so called paging. An AIT provides initial access related parameters for one or multiple areas. To reduce network energy consumption, the broadcasted signals are infrequent compared to reference signals in previous cellular systems, such as LTE. The AITs are typically transmitted with long periodicity, e.g. from 1.024 s up to 10.24 s.
FIG. 1b is a block diagram schematically depicting an example of a wireless communication network employing AITs and SSSs, such as discussed above and shown in FIG. 1a. In general, SSSs may not be node specific, instead one SSS may provide relevant access information for several nodes, as shown in the figure where small, e.g. pico, cells are associated with a SSS3 and larger, e.g. macro, cells covering the small cells, are associated with a SSS15. The larger cells may transmit access information related to the small cells. In order to enhance mobility, an AIT may contain access information related to adjacent areas. The system signature sequences provide time synchronization as well as a mapping to a table entry in the AIT. Typically SSSs are transmitted more often than AITs, e.g. every 100 ms.
In general, AITs and SSSs' are transmitted relatively seldom in time and frequency compared to conventional cellular systems. Some nodes may transmit both an AIT and an associated SSS, while some nodes only transmit an SSS.
A SSS may be similar, i.e. may be considered to correspond, to an LTE synchronization signal. Assuming that there are a total of 1024 possible SSSs then they can convey 10 bits of information. A received SSS-index is used for deriving access information from the AIT and received power used for layer selection and open-loop power control. The timing of a received SSS may be used for determining a Physical Random Access Channel (PRACH) transmission timing window.
It is realized that a wireless communication network, e.g. a 5G network, based on broadcasted AITs and SSSs as described above, has some advantages over existing, conventional wireless communication networks and conventional Radio Access Technologies (RATs), such as LTE, but that it is also faces challenges. For example, it is clearly advantageous that reduction of interfering and energy consuming signalling is enabled, e.g. reference signalling and signalling of various system information and the like. On the other hand, access to this information is often crucial. Any problem in accessing the “right”, desired information when it is need may impair performance. Worsened performance in any way compared to conventional wireless communication networks, will likely not be acceptable. The perhaps most crucial information is access information enabling a wireless device to access the wireless communication network through a radio network node.
Hence, it desirable that further development of and solutions for wireless communication systems, e.g. 5G networks, and that e.g. are supporting use of AITs and SSS as described above, reduces, or at least enable or facilitate reduction of, risks for performance degradation or other drawbacks, in particular with regard to access information, in relation to conventional wireless communication networks. At the same time it is of course desirable to also provide further advantages.